What's the Smartest Plant?

Compared to even the dumbest human being, your average tulip is a moron. But you’d have to be dumber than a tulip to deny that something – maybe not intelligence in its dictionary definition, but some guiding, autonomic power – is at work among the members of the plant kingdom. And if we grant plants this quasi-intelligence, then we have to concede that some of them must be smarter than others – cannier absorbers of bugs and sun, better users of their varied environments. Inevitably, then, the question is: which one’s smartest?

For this week’s Giz Asks, we asked a number of botanists and plant scientists for their take. No two named the same plant, or used the exact same definition of ‘intelligence’ – which is admittedly a tricky concept to pin down when you’re dealing with brainless cacti and pigweed. So if you’re looking for a straightforward list of nature’s sharpest greenery, this probably isn’t it – but then, you’re too smart to be looking for something as straightforward as that.

Katie Field

Associate Professor, Plant-Soil Processes, University of Leeds

A classic example of “plant smarts” might be the Venus Fly Trap (Dionea muscipula) which seems to count the number of times a hair is triggered on the surface of its trap before deciding to close on the unfortunate insect within. This “smart” behaviour makes sure it doesn’t waste energy closing its trap on something that isn’t insect prey – falling leaf litter, for example.

Of course, “smart” decisions aren’t limited to plants that move quickly. All plants have to respond to their environment, making decisions at physiological and molecular scales all the time in response to changes in their environment, both above and below ground.

For example, if water is scarce, the plant will close its stomata (tiny pores in the leaf surface that normally let water out) almost instantly. Whether or not these responses are “smart” or not is debatable, though.

A really cool phenomenon is the ability of plants to pick up underground signals from other plants via a shared network of symbiotic fungal hyphae (mycorrhizas). My favourite example of this is an experiment where beans that were infested with aphids stimulated uninfested neighbouring beans to produce defensive volatile chemicals that ward off the pests but attract wasps (aphid natural enemies). The only way this could have been possible in that experiment was via shared fungal connections between plants. It’d be tempting to say this was plant-plant communication, but really I think it was the fungus responding to changes in the infested host and then the non-infested host responding to changes in the fungus – but still, that’s a pretty smart response!

“A really cool phenomenon is the ability of plants to pick up underground signals from other plants via a shared network of symbiotic fungal hyphae.”

Patrick Keeling

Professor of Botany and head of the Keeling Lab at the University of British Columbia

I would turn this upside down and ask: how do you define “plant”? I work on algae and their close relatives. Lots of them are really smart.

Wornowiid dinoflagellates, for example, are single cells, but have tiny eyes with a lens and retina that they apparently use to hunt down prey. Their chloroplasts is now part of this eye, the part like a retina. When they find them, they use tiny poisonous harpoons called nematocysts to shoot and kill the prey cell, reel them in, and eat them.

Or there’s apicomplexans, like the malaria parasite Plasmodium. Also “algae,” or derived from them. They know how to infect us and beat our immune system. They get right inside our blood cells where the immune system can’t ‘see’ them, and then when they want to spread the whole population bursts out of their cell synchronously so they can quickly get inside another cell before the immune system can be alerted and react. Their chloroplasts is essential for infection and now makes lipids they need in their membranes.

Both those, I’d say, are pretty smart.

David Wees

Faculty Lecturer and Associate Director of the Farm Management and Technology Program at McGill University

The best adapted plants are generally what we humans call weeds. Ralph Waldo Emerson once said: “What is a weed? A plant whose virtues have not yet been discovered”. Indeed, weeds, despite the best efforts of farmers, gardeners, foresters and other folks, always seem to take advantage of every possible space to grow and multiply. They effectively compete with other plants for light, water and minerals.

I guess my vote for “smartest weed” would be quackgrass (Elymus repens), also known as couch grass or twitch grass. This grass is originally from Europe and western Asia. However, it has now spread to every continent, and has become a major weed on each one. Not only does it reproduce by seed, it also spreads by rhizomes, which are long, slender underground stems. Each piece of rhizome can produce a new quack grass plant – in effect a natural clone. If you plough a field with quackgrass, you will inadvertently cut up pieces of rhizomes which will then sprout, giving rise to more quack grass, and so on. Quack grass can grow in almost any type of soil (clay, sand, etc) or climate (although it is less common in tropical areas than in temperate climates). Once established in an area, it’s almost impossible to eliminate completely.

On the positive side, quack grass is great for controlling soil erosion on steep slopes. Indeed, its roots and rhizomes form a thick underground “mat” that holds on to soil particles. And because it grows vigorously, it is a good forage crop for livestock. For livestock, it is as good (nutritionally speaking) as most other grasses.

“It is from a group older than the dinosaurs, and hence has hung around with little change for 250+ million years, and yet still manages to outwit human begins, for all our supposed smartness, by being an almost ineradicable garden weed!”

Richard Milne

Lecturer, School of Biological Sciences, University of Edinburgh

I’m going to go for Equisetum arvense, the common horsetail, as an opening gambit. It has an impressive multi-purpose mechanism of spore dispersal, but the real reason I rate it so highly is that it is from a group older than the dinosaurs, and hence has hung around with little change for 250+ million years, and yet still manages to outwit human begins, for all our supposed smartness, by being an almost ineradicable garden weed! If pulled up, the underground stems simply break, effectively propagating the plant.

Philippa Borrill

Lecturer, Plant Biology, University of Birmingham

This may sound a bit kooky, but I think that crop plants are the smartest plants on the planet. We often think about crops as being domesticated by humans, but I would argue that the reverse is also true. The crops we depend on have domesticated (or perhaps even enslaved) us to sow their seeds for them, water and care for the growing plants, and then

harvest the seeds and make sure they get planted the next year (although obviously we do eat many of them too!).

In particular, wheat is grown on more land area across the world than any other crop. This is quite an amazing feat for a plant which originated in the fertile crescent, a relatively small area in the Middle East and Mediterranean about 10,000 years ago. Now humans sow wheat across five continents (North America, South America, Europe, Asia and Africa) and wheat has adapted to grow in a huge range of environments – from the hot, dry environment in Australia to the cool wet climate of the UK. Globally we produce 750 million tons of wheat every year, which equates to 1.5 x 1019 individual wheat grains (the ridiculously big number 15,000,000,000,000,000,000) and it provides food for over 2.5 billion people every day. If that’s not a smart plant I’m not sure what is.

Plants are able to do so many clever things: they can build their bodies from atmospheric gasses and sunlight; their seeds can persist in the soil for years (and in some cases centuries); they can woo animal pollinators to transport their gametes; and they do it all without a central processing organ analogous to a brain.

Olivia Wilkins

Assistant Professor, Plant Science, McGill University, and leader of the Plant Systems Biology research group

Plants are able to do so many clever things: they can build their bodies from atmospheric gasses and sunlight; their seeds can persist in the soil for years (and in some cases centuries); they can woo animal pollinators to transport their gametes; and they do it all without a central processing organ analogous to a brain. But given that these traits are common to most plants, I think the criteria that I’d used to pick out the smartest ones would be their ability to grow and thrive in unpredictable environmental conditions.

Most plants have evolved in the context of the long term climate of the areas in which they are endemic, and they grow well there. Plants that have been moved around by humans, like crops, have been bred to grow and produce (somewhat) reliable yields in a variety of site specific climates. But the challenge that plants are facing now is really hard. They are confronted by environments that are not only changing rather quickly, but which are punctuated by unfamiliar temperature and precipitation extremes. Some plants won’t be up to the challenge and they will become extinct. In the case of crops, this could be a disaster.

Fortunately, plants are already accustomed to responding to changing environments. Daily, they are confronted by energy rich periods of light and energy poor periods of darkness; they protect themselves against drying out by restricting their water use in dry times. They do this by employing flexible and dynamic subcellular structures called gene regulatory networks. One of my favourite examples of the power of regulatory networks to expand the environments in which plants can grow was discovered in rice. Most varieties of rice plants will die if they are completely submerged in water during the flash floods that can follow monsoons. But some rice varieties can tolerate complete submergence for more than a week. It turns out that plants that can tolerate submergence have a regulatory network controlled by a protein called sub1. Moreover, it turns out that if you move the gene encoding sub1 to rice varieties that are sensitive to submergence they become tolerant to it. Evolution has clearly targeted regulatory networks to expand the variety of conditions in which plants can grow, and I believe that these networks are the most accessible targets for defending plants against the new challenges presented by climate change.

But as for the question of which plant is the smartest? I don’t know. But I’m very hopeful that we’ll continue to discover and explore ways in which nature has already solved our most pressing plant questions.

David Duffy

Professor, Botany, University of Hawaii at Manoa

Plants are way smarter than people, who are just walking shadows; poor players, who strut and fret their hour upon the stage (to paraphrase the Bard). I’d say what makes a plant smart is surviving – like street smarts. Here are three examples.